Global setting: November 2018

11 January 2019

Sea surface temperatures (SSTs) across the east-central tropical Pacific have reached weak El Niño conditions. Over the past month, SSTs in the central Pacific (NINO3.4 Index) have continued to warm, increasing to an anomaly of +0.9oC. This marks the third consecutive month SST anomalies in the central Pacific have exceeded 0.7oC, which meets NIWA’S technical oceanic definition for El Niño.

However, the atmosphere has yet to respond to this additional warmth and become truly coupled with the ocean in a manner typically associated with an El Niño event. One reflection of this is the Southern Oscillation Index (SOI), which was at –0.2 for November, i.e. in the neutral range.

An El Niño event is considered to have formally occurred when the tropical Pacific Ocean and the overlying atmosphere act in concert and reinforce each other, operating as a key driver of global weather and climate patterns.

The consensus from international models is for the tropical Pacific to transition towards El Niño over the next three-month period (94% chance over December 2018 – February 2019). The probability for El Niño remains high through autumn 2019, with an 85% chance for occurrence in the March – May 2019 period. In fact, the probability of El Nino remains unusually elevated (66% chance) through to the next Southern Hemisphere winter season (signalling the possibility of a protracted El Niño event extending over 2 years).

Sea Surface Temperatures

Above average or near average sea surface temperatures (SSTs) are expected in New Zealand coastal waters during the next three months. Coastal SSTs are currently above average.

Differences from average November surface temperatures in the seas around New Zealand